Soundscapes under sea ice: Can we listen for open water?

Abstract

Different geophysical conditions at the ocean surface generate distinctive sound spectra underwater, thereby allowing the physical environment to be monitored using passive acoustics. In the central Bering Sea, a passive aquatic listener (PAL) was deployed on the NOAA M5 mooring through the 2008 and 2009 winter seasons, allowing the ambient sound under sea ice to be recorded. Distinctive features of sea ice soundscapes include loud sound levels during periods of ice formation and very quiet high-frequency levels during periods of solid ice coverage. These soundscapes do have distinctive spectra features that distinguish them from other geophysical conditions, including wind-generated spectra, drizzle, and rainfall onto open water. This indicates that it is possible to listen for ice-free surface conditions. In turn, this will allow sub-surface ocean instrumentation on drifters, profilers, or moorings to detect open water and surface during relatively safe ice-free surface conditions (by listening), thus minimizing damage risk and allowing data transfer by satellite data links, an important advance for engineering oceanographic studies in ice covered seas. [Work sponsored by ONR Marine Mammals.]